Ask the Doctors

Dear Doctor: How bad are trans fats really? Seems hard to believe that simply banning them in restaurants could cut heart attacks and strokes, as a recent study suggests.

Dear Reader: First, let's start with hydrogenation, a process that adds hydrogen to the fats found in vegetable oils in order to make them solid. A partial hydrogenation process creates trans fats. Trans fats have a long shelf life, are more stable when fried and can make baked goods taste more palatable. That sounds good, doesn't it?

The reality is less so. For starters, trans fats negatively impact cholesterol levels by increasing LDL cholesterol (the bad cholesterol linked to heart disease) and decreasing HDL cholesterol (the good cholesterol that protects against heart disease). If that weren't enough, trans fats also increase triglycerides, lipoprotein(a) and small particles of low-density lipoprotein (LDL), all of which increase the risk of heart disease.

Further, trans fats increase inflammation throughout the body, raising levels of inflammatory markers, such as tumor necrosis factor (TNF), interleuken-6 and C-reactive protein. That's important because increased inflammation is a risk factor for diabetes, atherosclerosis, heart failure and sudden cardiac death. What's more, trans fats have a direct effect on the inner lining of blood vessels, which may further increase the risk of heart attacks and strokes.

The evidence as to trans fats' negative impact is growing. A combined New England Journal of Medicine analysis of four studies, based on nearly 140,000 subjects' dietary habits, found a clear link between consumption of trans fats and coronary heart disease. The researchers found that a 2 percent increase in daily caloric intake from trans fats led to a 23 percent risk in coronary heart disease.

Similarly, an 11-year study published in the journal Circulation evaluated blood samples of people who had experienced sudden cardiac arrest and compared them to blood samples of people in the community. Those patients who had elevated trans fats in the membranes of red blood cells had a 47 percent greater risk of sudden cardiac arrest. Most of this increased risk was seen in people with elevated linoleic trans fatty acids, meaning that some artificial trans fats are worse than others. Note that some trans fats are produced naturally in the stomach of cows and some end up in small amounts in cow milk; these types of trans fats have not been associated with heart disease.

As for the recent study published in JAMA Cardiology, it concluded that restaurant bans of trans fats could save lives. Researchers looked at hospital admissions for heart attack and stroke in New York counties with restaurant bans and compared the numbers to those in counties without restaurant bans. They found that even eliminating only restaurant trans fats from one's daily diet cut heart attacks by 7.8 percent and strokes by 3.6 percent.

Obviously, there are many possible confounding factors to this study, but the conclusion from the overall body of evidence is hard to ignore: Eliminating trans fats will decrease your chance of premature death.